JP2024050570A - Recycling method for composite materials with improved energy balance - Google Patents

Abstract

A method for recycling an article made of a composite material is provided, comprising the steps of: feeding an article (201) containing a composite material including a polymer matrix and a reinforcing material into a reactor (202) for heating the article; heating the article in the reactor to a predetermined temperature to decompose the polymer matrix; separating the reinforcing material (209) from the decomposed polymer matrix; and contacting the reinforcing material with a first heat transfer means to recover heat.Selected Figure:

Description

The present invention relates generally to the recycling of articles made of composite materials, and more specifically to a method for recycling composite materials with improved energy balance.

The invention is useful in all industrial sectors facing the problem of recycling complex post-consumer waste, such as used products, or industrial waste, such as defective products or scrap resulting from plastics processing operations.

Prior Art

A composite material (also abbreviated as "composite") is a macroscopic combination of at least two materials that are immiscible with each other. In general, a composite material is composed of a polymer matrix, which forms a continuous phase, on the one hand, and a reinforcing material (or reinforcement), which is generally a fibrous reinforcement, on the other hand. There are also composites consisting of a polymer matrix and mineral fillers, such as quartz, marble, silica, aluminum hydroxide, _TiO2 , etc. In some cases, composite materials also contain additives. Furthermore, these materials are often combined with other components, such as metal inserts, wood or foam, to manufacture articles for various industries.

Recycling of composites based on a polymer matrix or articles containing polymer composites can be carried out by several methods. These methods generally involve the pyrolysis of the polymer, that is, the loss of its mechanical and physical properties due to the action of heat or an increase in the temperature of the polymer.

Pyrolysis is known and is a thermal process consisting of placing the article to be treated in a suitable chamber and then heating the chamber to transfer heat to the article. The pyrolysis temperature is generally between 400°C and 1300°C to allow chemical decomposition of the polymer matrix. Pyrolysis of the article results in the formation of gases, oily residues and solid residues including reinforcements of composites, inorganic fillers and carbonaceous solids. The gases obtained after pyrolysis can be reused for the manufacture of new polymer articles and the solid residues obtained after pyrolysis are reused in the manufacture of other products such as insulating materials in particular. This recycling method has a poor energy balance.

Fluidized bed processes are also known, where the fluidized bed can be, for example, a bed of silica sand. In this process, the article containing the composite is generally pre-ground and placed in a fluidized bed reactor containing a fluidized bed. Fluidization is carried out using a gas flow, generally heated to a temperature above 400° C. In this bed, the matrix is rapidly heated and gasified, removing the reinforcement from the matrix. A part of the reinforcement is then carried out from the bed in the gas flow to a secondary combustion chamber. Another part is entrained with the solids that make up the fluidized bed and is taken to a vessel where the solids are reheated, and the carbonaceous residue is burned before being returned to the fluidized bed reactor. As in the case of pyrolysis, the method is not designed to optimize its energy balance. In both cases, at the end of the depolymerization/gasification, the solids that make up the reinforcement are discharged and the heat that they had accumulated is lost. The more heat lost, the greater the mass of non-depolymerizable/non-gasifiable material.

The chemical treatment of composite articles by solvolysis is also a known recycling method. It consists in treating the composite material of the article with a suitable solvent to allow the depolymerization of the polymer matrix. This can be carried out at temperatures below 200 °C or under supercritical conditions at temperatures above 200 °C and high pressure (above 200 bar). Solvolysis can be seen as a "decomposition" of the composite material, which gives, on the one hand, an inorganic fraction that contains in particular the reinforcement of the composite material, and, on the other hand, a liquid solution that contains the products resulting from the depolymerization and the solvent. At the end of the solvolysis process, the reinforcement and the polymer solution can be reused.

Known methods for recycling articles containing composite materials appear to involve various heating steps, consisting, for example, of heating a solvent for solvolysis, or heating a gas to fluidize a sand bed, or heating a reactor to induce pyrolysis. These various heating steps require the input of energy in the form of heat, and an undesirable consequence is the consumption of a significant portion of energy for heating the fibrous reinforcement and mineral filler (or any other non-depolymerizable/non-gasifiable material) contained in the composite. In particular, composite materials may contain up to 70% by weight or more of non-depolymerizable solid compounds constituting the fibrous reinforcement, such as, for example, glass fibers. The amount of energy expended on heating these non-depolymerizable solid compounds must therefore be seen as a loss in the energy balance of the operation.

From an energy and environmental perspective, it would therefore be desirable to have a recycling method that allows for an improved energy balance.

Document EP 2 752 445 A1 describes a method and an apparatus for recycling composite materials comprising a polymer matrix and carbon fiber reinforcement. The aim of this document is not to degrade the carbon fibers during the recycling of the composite material so that it can be recycled in a process for producing nonwoven fabrics. The composite article to be recycled is introduced into a reactor where it is heated to decompose the structure of the polymer matrix.

Document JP3899563 describes the recycling of composite materials containing a polymer matrix and a fibrous reinforcement made of glass fibers.

For this, the material to be recycled is placed in a reactor and heated below the melting point of the glass fibre until the combustion of the organic matter progresses and the amount of carbon residue is reduced.

Document WO 2017/178681 describes a method for recycling composite materials containing fibrous reinforcement made of carbon and/or glass fibers. The composite material is introduced into a horizontal reactor containing three independent zones separated from each other by a separating gate.

The document DE 10 2007 026 748 describes a method and an apparatus for the continuous recycling of carbon fiber reinforced composite materials. For this, the material is conveyed to a tunnel reactor which comprises a preheating chamber, a pyrolysis chamber and a reheating chamber.

Technical challenges

The object of the present invention is to eliminate at least one of the above-mentioned shortcomings of the prior art.

The present invention aims in particular to provide a simple and effective solution for depolymerizing the constituent polymers of composite articles, improving the energy balance and in particular making it possible to recover the heat absorbed by the solid non-depolymerizable fibrous material.

To this end, in a first aspect of the invention, there is provided a method for recycling an article comprising a composite material, the composite material comprising a polymer matrix and a reinforcing material, the method comprising the steps of:
- placing the article in a reactor suitable for heating the article;
- heating the article in the reactor at a predetermined temperature to decompose the polymer matrix;
A method is proposed, characterized in that it comprises a step of separating the reinforcement from the decomposed polymer matrix, and a step of contacting the reinforcement with a first heat transfer means in order to recover the heat.

It is thus possible to transfer the sensible heat stored in the reinforcement with the aim of reusing this heat. This heat must be further recoverable at one or more heat levels in order to be able to reuse it in downstream operations for purifying the resulting monomers or in upstream operations for drying the material. Thus, the method makes it possible to carry out the recycling of articles containing composite materials with a reduced carbon footprint. The method according to the invention is therefore more environmentally friendly.

Furthermore, the method according to the invention is particularly advantageous for composites containing more than 40% by weight of reinforcement, preferably more than 50% by weight of reinforcement, more preferably more than 60% by weight of reinforcement, advantageously more than 70% by weight of reinforcement.

According to another optional feature of the method,
- the goods are fed into the reactor by an endless screw, a conveyor belt, a hopper or a weighing module;
- the article is heated at a temperature between 200°C and 1500°C;
the reinforcement is separated by at least one of the following processes: centrifugation, draining, spinning, pressing, filtering, screening and/or cyclones;
the first heat transfer means is a heat exchanger in which there is direct contact between the reinforcement and the heat transfer fluid;
the first heat transfer means is a device for immersion in a heat transfer fluid or for spraying a heat transfer fluid;
- the first heat transfer means is a heat exchanger in which there is indirect contact between the reinforcement and the heat transfer fluid;
- a protective agent is added to the reinforcement;
- the recovered heat is used in the article recycling process in addition to the heat injected by an external heat source;
- The recovered heat is used to preheat the goods before they enter the reactor;
the method further comprises, after the heat recovery by contacting the reinforcement with the first heat transfer means, a step consisting of contacting the reinforcement with a second heat transfer means in order to recover additional heat;
- the polymer matrix comprises polymethyl methacrylate (PMMA);
A part of the decomposed matrix is reintroduced into the reactor after being separated from the reinforcement, which on the one hand may allow a faster decomposition of the matrix of the next article and on the other hand may allow an improved recycling of the reintroduced matrix.

The present invention also provides a system for recycling an article comprising a composite material having a polymer matrix and a reinforcement, the system comprising:
- means for conveying said articles,
a reactor suitable for heating said article in order to decompose its polymer matrix;
- means for separating the reinforcement from the decomposed polymer matrix; and - first heat transfer means suitable for recovering heat from the reinforcement.

The recycling system of the present invention may further include a second heat transfer means capable of recovering additional heat from the reinforcement material.

Other characteristics and advantages of the invention will become apparent from the following description, given by way of example and without implied limitation, with reference to the attached figures in which:
A process diagram of a recycling method according to one embodiment. FIG. 2 shows an example of heat transfer by a direct contact heat exchanger; Diagram of a plate heat exchanger, and FIG. 4 is a process diagram of a recycling method according to another embodiment.

In the remainder of the description, the term "monomer" is understood to mean a molecule capable of undergoing polymerization.

The term "polymerization" as used refers to the process for converting a monomer or mixture of monomers into a polymer.

The term "polymer" is understood to mean either a copolymer or a homopolymer. A "copolymer" is a polymer that groups together several different monomer units, and a "homopolymer" is a polymer that groups together identical monomer units.

The term "depolymerization" as used refers to a process for converting a polymer into one or more monomers and/or oligomers and/or polymers having a reduced molecular weight compared to the molecular weight of the original polymer.

"Reduced polymer" is understood to mean a polymer whose weight average molecular weight is lower than the weight average molecular weight of the original polymer that constitutes the matrix. The weight average molecular weight can be measured by size exclusion chromatography.

"Thermoplastic polymer" or "thermoplastic" is understood to mean a polymer that can soften or melt under the action of heat in a repeated manner and assume new shapes by the application of heat and pressure. Examples of thermoplastics are, for example, high density polyethylene (HDPE), used in particular for the manufacture of plastic bags or in the manufacture of automobiles; polyethylene terephthalate (PET) or polyvinyl chloride (PVC), used in particular for the manufacture of plastic bottles; polymethyl methacrylate (PMMA). Thus, the use of thermoplastics affects various sectors, from packaging to the automotive industry, and the demand for plastics remains high.

"Thermosetting polymer" is understood to mean a plastic material that is irreversibly transformed by polymerization into an insoluble polymer network.

"(Meth)acrylic polymer" is understood to mean a homopolymer or copolymer based on (meth)acrylic monomers selected, for example, from methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, methacrylic acid, acrylic acid, n-butyl acrylate, isobutyl acrylate, n-butyl methacrylate, isobutyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate and mixtures thereof. Poly(methyl methacrylate) (PMMA) is a specific example of a (methacrylic)polymer obtained by polymerization of the methyl methacrylate monomer.

For the purposes of the present invention, the term "PMMA" refers to homopolymers and copolymers of methyl methacrylate (MMA), and in MMA copolymers, the weight ratio of MMA in PMMA is preferably at least 70% by weight. The term "copolymer based on methyl methacrylate" refers to a copolymer comprising at least one methyl methacrylate monomer. For example, a copolymer based on methyl methacrylate may be a copolymer comprising at least 70% by weight, preferably 80% by weight, advantageously 90% by weight of MMA in PMMA.

The term "base monomer" refers to the most predominant monomer unit that makes up a polymer. Thus, in PMMA, the base monomer is MMA.

"Polymer matrix" is understood to mean a solid material that acts as a binder. "Matrix" includes polymers and/or oligomers. Thus, "(meth)acrylic polymer matrix" relates to any type of acrylic and methacrylic compound, polymer, oligomer or copolymer. However, it does not constitute a departure from the scope of the invention if the (meth)acrylic polymer matrix contains up to 10% by weight, preferably less than 5% by weight, of other non-acrylic monomers, for example selected from the following group: butadiene, isoprene, styrene, substituted styrenes such as α-methylstyrene or tert-butylstyrene, cyclosiloxanes, vinylnaphthalene and vinylpyridine.

For the purposes of the present invention, "composite" is understood to mean a multicomponent material comprising at least two immiscible components, at least one of which is a polymer and the other of which may be, for example, a fibrous reinforcement.

"Reinforcement" is understood to mean non-depolymerizable or non-gasifiable solid materials such as "fibrous reinforcement" or "mineral fillers" that remain at the end of the process.

"Fibrous reinforcement" is understood to mean an assembly of fibers, unidirectional rovings or continuous filament mats, woven fabrics, felts or nonwoven fabrics, which may be in the form of strips, webs, braids, rovings or parts.

The term "mineral fillers" is understood to mean all powdery fillers, such as quartz, marble, silica, aluminum hydroxide or _TiO2 .

The term "decomposition (structural decomposition)" is understood to mean a process in which the matrix polymer of the composite material is treated to become a molten mixture and/or a gaseous mixture, thus making it possible to liberate the fibrous reinforcement. Decomposition can result in depolymerization, which is a process in which the matrix polymer is fragmented to become a molten mixture and/or a gaseous mixture. The fragmentation of the polymer can in particular lead to the base monomers of the polymer.

"Heat exchanger" is understood to mean a system for transferring heat between a first component and a second component, the first component having a higher temperature than the second component.

"Direct contact heat exchanger" is understood to mean an exchanger in which there is no partition between the first and second components.

"Indirect contact heat exchanger" is understood to mean an exchanger in which the first component is not in contact with the second component, e.g. the hot reinforcement material is not in intimate contact with the fluid.

For the purposes of the present invention, the term "substantially equal" is understood to mean a value that varies from the compared value by less than 30%, preferably less than 20%, and more preferably still less than 10%.

In the following description of the embodiments and the accompanying drawings, the same reference numerals are used to indicate the same or similar components.

The present invention also relates to a method for recycling an article made of a composite material, the composite material of the article to be recycled comprising at least one polymer matrix and a reinforcing material.

The polymer matrix can be a thermosetting polymer matrix or a thermoplastic polymer matrix.

Thermosetting or thermosetting polymers are polymers with a cross-linked three-dimensional structure. Thermosetting polymers are molded and cross-linked into the desired shape when exposed to high temperatures. Once the shape of a thermosetting polymer is fixed and cooled, it cannot be changed under the action of heat. Thermosetting polymers are, for example, unsaturated polyesters, polyimides, polyurethanes, or vinyl esters that can be epoxy or phenolic.

Matrices based on thermoplastic polymers are generally preferred because they are thermoformable and more easily recyclable. By way of non-limiting example, thermoplastic polymer matrices include olefin homopolymers and copolymers, such as acrylonitrile-butadiene-styrene copolymers, styrene-butadiene-alkyl methacrylate (or SBM) copolymers; polyethylene, polypropylene, polybutadiene, and polybutylene; acrylic homopolymers and copolymers, and polyalkyl methacrylates, such as poly(methyl methacrylate); homopolyamides and copolyamides; polycarbonates; polyesters, including poly(ethylene terephthalate) and poly(butylene terephthalate); polyethers, such as poly(phenylene ether), poly(oxymethylene), poly(ethylene terephthalate ... (oxyethylene) or poly(ethylene glycol) and poly(oxypropylene); polystyrene; copolymers of styrene and maleic anhydride; poly(vinyl chloride); fluoropolymers such as poly(vinylidene fluoride), polyethylene tetrafluoride and polychlorotrifluoroethylene; natural or synthetic rubber; thermoplastic polyurethanes; polyaryletherketones (PAEKs), such as polyetheretherketones (PEEK) and polyetherketoneketones (PEKK); polyetherimides; polysulfones; poly(phenylene sulfide); cellulose acetate; poly(vinyl acetate); or mixtures of two or more of these polymers.

In particular, the thermoplastic polymer matrix can be poly(methyl methacrylate) (PMMA) resin.

In composite materials, a thermoplastic polymer matrix is intimately bonded to a reinforcement. The reinforcement can be seen as a strengthening means, often based on glass or carbon fibres. For example, the reinforcement can be a fabric, web, felt or fibrous material, for example based on glass fibre, carbon fibre or basalt fibre. In particular, the composite material of the recycled article is based on PMMA and fibrous material.

During recycling of articles containing composite materials, the polymer matrix is decomposed or depolymerized.

Recycling of articles containing composite materials, and more specifically decomposition of composite materials, can be carried out by methods such as pyrolysis, high temperature pyrolysis, heat treatment in a fluidized bed reactor, heat treatment in an extruder or conveyor, heat treatment in a rotary kiln, pyrolysis in a mechanically stirred bed, pyrolysis in a molten salt bath, or depolymerization by solvolysis involving elevated temperature.

1 shows a flow diagram of a method for recycling articles according to a first embodiment. This recycling can be seen as a method in which the polymer matrix of a composite material is converted to obtain a molten and/or gaseous residue and a solid residue containing the reinforcement is produced. For this purpose, in step 110, the article to be recycled is introduced into a reactor suitable for polymer recycling. The article is then heated in step 120 using a suitable heating means. For example, heating can be performed by exposing the article to a molten lead bed, a fluidized bed (e.g. sand), microwaves, a pulsed electric field or steam, or by contact with a hot surface, as in an extruder, a screw conveyor, etc. The hot surface can be heated by various means, such as direct electrical heating, heating with a heat transfer fluid (steam, oil, molten salt, etc.). The article is heated at a given temperature that allows the decomposition of the composite material and results in at least one molten and/or one gaseous residue. Heating is carried out, for example, at a temperature between 200°C and 1500°C, preferably between 200°C and 600°C, more preferably between 200°C and 500°C, and more preferably still between 300°C and 500°C.

Depolymerization of the composite also results in the formation of a solid residue that includes the reinforcement. In step 130, the reinforcement is separated from the decomposed polymer matrix. This reinforcement is then contacted in step 140 with a first heat transfer means such that heat stored by the reinforcement is transferred to a fluid, which can be a liquid or a gas.

Furthermore, if the depolymerization is not carried out to a degree of conversion of 100%, the non-depolymerized or non-gasified polymer fraction may store heat and transfer it back to the first heat transfer means. Thus, if the depolymerization is not carried out to a degree of conversion of 100%, the method includes a concomitant step during which the non-depolymerized fraction is contacted with the first heat transfer means. In that case, the sensible heat and/or heat of fusion of the polymer stored by the non-depolymerized fraction may be transferred to the fluid, which may be liquid or gas, following the same sequence as the reinforcement. Furthermore, the method may include an additional step in which the non-depolymerized fraction may be fully or partially oxidized to generate heat of combustion that is recovered by the heat transfer means. This additional step may or may not involve the recovery of sensible heat from the reinforcement. Thus, the heat recovery from the non-depolymerized fraction makes it possible to further improve the overall energy balance.

Advantageously, according to this method, after the step of purifying the MMA resulting from the depolymerization, it is also possible to recover the heat of combustion stored by the impurities of the depolymerization. It is thus possible to transfer the heat stored in the reinforcement, the non-depolymerized fraction, or the impurities with a view to reusing this heat.

The heat thus recovered is advantageously recovered at one or more heat levels in order to maximize its use in downstream operations for purifying the monomers obtained or in upstream operations for drying or preheating the materials. Thus, the method makes it possible to carry out the recycling of articles containing composite materials with a reduced carbon footprint and reduced energy consumption of non-renewable resources. The method according to the invention is therefore more environmentally friendly.

It should be noted that the items to be recycled may be manufactured products or parts of manufactured products at the end of their life, or waste from the manufacture of such products. In either case, a prior sorting step may prove necessary to eliminate non-depolymerizable waste or non-depolymerizable products that contribute to reduced energy efficiency.

In one embodiment, the method for recycling articles includes a pre-sorting step before carrying out the method described above with reference to the process diagram of FIG. 1. The sorting step can be a step in which articles containing composite materials are separated and sorted. For example, it can be separated and sorted from articles not containing composite materials and/or it can be separated and sorted from contaminants such as glass, sand or metal. The sorting step also allows for the separation and sorting of plastics by households. For example, it is possible to sort thermoplastic polymers on the one hand and thermosetting polymers on the other hand. Sorting can also make it possible to exclude parts resulting from the grinding that are not made of composite materials.

Sorting can be carried out by any sorting method suitable for recycling polymers. One possible sorting method can include a decantation system, where the waste is placed in a tank of water and/or brine. The heavy components are found at the bottom of the tank and can be discharged by a pneumatic airlock system. The components to be recycled can be removed from the tank using an endless screw. Sorting can also include magnetic sorting to remove metal particles. Sorting can also include eddy current separation to remove certain metals such as copper. Separation techniques can also be combined, for example sorting by density in solution and magnetic separation. Sorting can be carried out in a sorting center. The sorting process advantageously makes it possible to discharge components that may damage the various equipment used to carry out the recycling method.

A dosing means can be used to feed the recycled goods to a reactor suitable for polymer recycling. For example, the goods can be fed to the reactor by an endless screw, a conveyor belt, a hopper or by a weighing module. The flow rate for feeding the recycled goods to the reactor can be between 10 kg/h and 2000 kg/h, preferably between 50 kg/h and 500 kg/h, preferably between 100 kg/h and 400 kg/h.

To facilitate the introduction of the article into a reactor suitable for recycling the polymer, the article can be pre-comminuted. Thus, in one embodiment, the method for recycling an article comprises a step of comminuting the article, carried out before step 110 of FIG. 1. The comminuting step makes it possible to reduce the size of the article to be recycled and can be carried out, for example, using any suitable mechanical grinder. The article is reduced to a size that allows the obtained ground material to be introduced into an apparatus suitable for recycling according to the invention. The particles obtained after comminution can have, for example, a size such that at least one dimension is between 1 mm and 100 mm, preferably between 3 mm and 50 mm. Preferably, at least one of the dimensions is less than 3 mm. The article can then be in the form of chips, granules or powder. The article can also be introduced into the reactor in one or more of the above forms. Advantageously, the comminuting step can make it possible to facilitate the sorting step. For this reason, the comminuting step can be carried out before the above-mentioned sorting operation.

Advantageously, the method for recycling an article comprises a step of preheating the article to be recycled. This step of preheating the article can be carried out before feeding it into the reactor and, if appropriate, after comminution. Preheating can be carried out using any suitable heating means. In one variant, preheating can begin in a reactor suitable for polymer depolymerization. The temperature to which the article is preheated can be 50° C. or higher, for example 200° C. Preheating the article can convert part of the polymer into a molten or liquid state and/or facilitate the depolymerization of the polymer matrix. Advantageously, preheating of the article can be carried out by heat recovered by heat transfer means from heat recovered on site. In this case, energy savings are achieved and the method has a favorable energy balance, making it more environmentally friendly. Furthermore, the rate of depolymerization increases when the article is preheated, thus making the recycling process generally faster.

To recycle the composite article and to decompose the polymeric part of the composite, the article is placed in a reactor. For example, the reactor can be an extruder or a conveyor, a reactor suitable for pyrolysis, high temperature pyrolysis, pyrolysis in a molten salt bath, or a fluidized bed reactor or a reactor suitable for solvolysis or a reactor consisting of hollow plates heated by a heat transfer fluid circulating inside the plates.

The extruder-conveyor is a reactor comprising one or more endless screws each operated in a barrel, which in particular allows mixing of the components introduced into said barrel. The use of an extruder-conveyor to carry out the recycling method is advantageous from the environmental, security and safety points of view of the process. In particular, the extruder-conveyor makes it possible to process molten polymers of high viscosity without the need to add solvents to reduce the viscosity of the molten polymer. The extruder-conveyor has the advantage of allowing efficient heat transfer from the barrel to the composite being processed. The extruder can advantageously be replaced by a screw conveyor system over the whole or part of its length. Advantageously, the system can comprise a combination of a first part of a conveyor type device, a subsequent extruder type device and a conveyor type device configured to transport the final solids (i.e. the reinforcement) to the discharge.

The reactor for receiving the recycled articles containing composites can be a circulating fluidized bed reactor. A circulating fluidized bed reactor is a reactor in which the fluidization velocity in the transfer section of the fluidized bed is of the order of 4 to 8 m/s, i.e. faster than that of conventional fluidized beds, which are 0.4 to 1 m/s. In this type of reactor, the high-velocity fluidized bed is at the bottom, and above it there is a smaller diameter section. In the lower section, the composite and the heat transfer solids are intensively mixed, allowing efficient heat transfer. The depolymerization/gasification produces an additional amount of gas, which then flows upwards, entraining the composite and the heat transfer solids. At the top of the reactor, a discharge zone allows the heat transfer solids to be returned to the vessel for reheating, and the produced gases and also the fibers and other solids to be removed. This device has the advantage that it allows good heat exchange between the entrained solid particles.

Reactors suitable for recycling the articles can also be pyrolysis reactors, for example multi-stage pyrolysis reactors or stirred rotating cylinder reactors. Two configurations are possible: either the cylinder rotates on its axis or an internal stirring system ensures mixing.

Another example of a reactor suitable for recycling articles can be a high-temperature pyrolysis reactor. Such a reactor contains a vitreous suspension and the processing temperature of the articles is between 1200°C and 1500°C. Upon exiting the reactor, glass granules are recovered, especially if the composite material is based on glass fibers.

A reactor that can be used to recycle articles containing composite materials can be a reactor for pyrolysis in a molten salt bath, where depolymerization generally occurs between 400°C and 500°C. The article is immersed in the molten salt bath to allow depolymerization of the matrix. The fibers can be recovered, for example, by filtration from the salt bath. The salt bath can consist of a eutectic mixture, such as eutectic _CaCl2 or eutectic NaCl _{- Na2CO3} . Advantageously, pyrolysis in a molten salt bath is suitable for treating composite materials contaminated, for example, with thermosetting polymers or with paints or varnishes.

Another type of reactor that can be used consists of hollow plates heated by a heat transfer fluid circuit (pressurized steam, oil, molten salts, etc.). During the course of its treatment, the articles advance over the plates, which in the first stage increase in temperature. The solid residues finish their passage through the reactor by passing through plates that are at a lower temperature and where heat exchange from the residue to the heat transfer fluid takes place. The heat transfer fluid thus reheated can then be used to preheat the articles at the reactor inlet.

In all the reactor examples discussed above, the article made of the composite material is heated in the reactor to a given temperature that allows the decomposition or depolymerization of the constituent polymers of the composite material. Such a temperature can be between 200°C and 1500°C, depending on the type of reactor and the decomposition technique used. In the case of a composite containing PMMA, the given decomposition temperature can be between 300°C and 600°C, preferably between 350°C and 500°C, more preferably between 400°C and 450°C, this temperature range being particularly suitable for the decomposition of the polymer of interest, PMMA.

In a preferred embodiment, the heating of the article is carried out under an inert atmosphere, for example under vacuum, _nitrogen , CO2 or argon, or under an atmosphere substantially low in oxygen (for example 0.1% to 10% oxygen). Alternatively, if production of synthesis gas by gasification is desired, the heating of the article is carried out in the presence of a reactive gas, including oxygen. To control the atmosphere in which the heating of the article is carried out, the reactor can be partitioned from the feed by a feedlock, or for example by a plug of molten polymer, or by any other means. Thus, the reactor into which the article is introduced can be partitioned gas-tight during its operation, more particularly during the heating/pyrolysis/depolymerization steps. By way of example, the oxygen composition in the reactor can be controlled and adapted to the properties of the composite. Such an oxygen-depleted atmosphere can be obtained, for example, by recycling the combustion gases of the light effluent from the depolymerization unit. After combustion, the oxygen content can be brought to a suitable range.

In the recycling method according to the embodiment, it is envisaged that the polymer matrix is decomposed and converted, for example, into a mixture in the molten or liquid state or into a mixture in the gaseous state. The method thus includes a separation step in which the reinforcement and the decomposed matrix are separated and partitioned from one another. The separation means are adapted to the state of the matrix in the reactor or at the outlet of the reactor, i.e. depending on whether the matrix is converted into the mixture in the molten or liquid state or into the mixture in the gaseous state. If the reinforcement is included in the mixture in the molten or liquid state, the separation means can be any means that allows solid-liquid separation, for example a grid. The separation can also be carried out by centrifugation using a centrifuge, or by decantation, filtration, draining, spinning, pressing or screening. Preferably, the separation is carried out by filtration, pressing or decantation in the molten medium. If the matrix is gasified/depolymerized, the separation means can include, for example, a cyclone or a filter. If a filter is used, a back pressure is periodically applied to loosen the solids accumulated in the filter. The solid cake is then collected under a filter in a container provided for this purpose. It should be noted that during the depolymerization of the matrix, polymer residues may remain in the reinforcement.

In some cases, a part of the decomposed matrix is reintroduced into the reactor. In particular, during the separation step, the mixture in the molten or liquid state can be recovered in a chamber provided for this purpose. In the case of a mixture in the gaseous state, the gas can be withdrawn from the reactor through a duct in order to be condensed in a condenser provided for this purpose. The chamber containing the mixture in the molten or liquid state can for example be connected to the reactor via a return duct or leg in order to allow the mixture to be reintroduced into the reactor. The mixture in the molten state contains in particular light polymers. Thus, advantageously, the reintroduction of the mixture in the molten state resulting from the decomposition of the matrix makes it possible to facilitate the decomposition of the matrix of the next article or the next batch of articles and/or to improve the degree of conversion of the matrix. Furthermore, the condensation of the gas mixture can be carried out fractionally, resulting in a clean fraction containing the base monomer and a less clean fraction containing the monomer and the contaminants. This fraction containing the contaminants can also be reintroduced into the reactor in order to allow a better separation of the monomer contained in this fraction.

In this recycling method, the reinforcement obtained after the steps of separating and sorting the reinforcement is contacted with a first heat transfer means and optionally a second heat transfer means.

The heat transfer means is advantageously a heat exchanger. In general, a heat exchanger allows the transfer of heat between two fluids. In the present recycling method, the heat transfer takes place between a solid and a heat transfer fluid. The solid and the fluid may be stationary or both may be moving, otherwise the solid may be stationary and the fluid may be moving. The solid and the fluid may circulate parallel to each other and in the same direction. However, the solid and the fluid may circulate parallel to each other but in opposite directions. They may also circulate orthogonally.

The heat transfer can be performed by a direct contact heat exchanger. Thus, during the heat transfer performed by a direct contact heat exchanger, the hot reinforcement is in intimate contact with a heat transfer fluid. The fluid can be a liquid, for example, water, a solvent or a mixture thereof. In another example, the fluid can be a gaseous fluid, for example, air or a gas stream. The contact with the fluid can be performed using an immersion or spraying device. Preferably, the contact is made by spraying to generate hot steam. This spraying can be followed by immersion. The contact can also be performed by a nozzle or a series of nozzles with holes through which the fluid can escape, the nozzles being directed at the solid components. Other heat transfer fluids can also be used; preferably, fluids available on site are used. For example, water, air, gas, and by-products of the depolymerization, especially hydrocarbons, can be used as fuel oil and/or secondary heat transfer fluids. In particular, the hydrocarbons, like water, vaporize when they come into contact with the hot residue. The hot gas is directed to a boiler, where the hydrocarbons are condensed and the water boils. This water will be used in the process or to heat the primary heat transfer fluid.

In a variant, the heat transfer can be carried out by an indirect contact heat exchanger. Such a heat exchanger can be, for example, a tube exchanger, a plate exchanger, an exchanger with a horizontal tube bundle, an exchanger with a vertical tube bundle, a spiral exchanger, a finned tube exchanger, or a rotary or block exchanger. These examples are not limiting and the skilled person will understand that other types of indirect contact heat exchangers can be used. Indirect contact heat exchangers can also use a heat transfer fluid. The heat transfer fluid can be a liquid, for example water, a solvent or a mixture thereof, a molten salt, or a synthetic oil. For example, such a synthetic oil can be a product sold by Arkema under the name Jarytherm®.

The advantage of indirect contact heat exchangers is that they allow heat recovery at various heat levels. In other words, it is possible to recover heat at several heat levels, each associated with a different temperature. Heat exchangers can be cascaded (or multi-staged) to allow for heat exchange with reinforcement that does not get too hot from one exchanger to the next.

To carry out this recycling method, in particular
- means for conveying said composite article,
a reactor suitable for heating said article with a view to decomposing its polymer matrix;
It is possible to use a system comprising: - a means for separating the reinforcement from the decomposed polymer matrix; and - a first heat transfer means suitable for recovering heat from the reinforcement.

A recycling method in which the reactor is a fluidized bed reactor is described below. With reference to the schematic diagram in FIG. 2, the article 201 made of a composite based on PMMA and fibers is fed by a hopper or an endless screw 216 into a fluidized bed reactor 202, preferably into the lower part of the reactor (as the article 201 tends to rise in the fluidized bed). The article 201 is in the form of particles of about 25 mm obtained by grinding (not shown).

An inert fluidized medium is also charged into the reactor. This medium can be, for example, sand, ceramic particles, metal particles, metal oxide particles, metal hydroxide particles, or metal halide particles.

The inert particulate medium and the article 201, in the form of crushed particles, form a mixture of solid particles 203 suspended in a hot ascending gas stream 204 on a distribution support/grid 205. The inert particulate medium is reheated by the hot gas stream and/or in an external vessel (not shown). In the latter case, the solids present in the reactor 202 are withdrawn, for example by an endless screw, to be reheated in an external vessel before being returned to the reactor 202. Reheating can be performed by combustion of carbonaceous residues of the article 201 and/or by external heat input.

The gas stream may be based, for example, on nitrogen, carbon dioxide, monomer or steam, optionally heated to a temperature between 450°C and 550°C.

The support 205 can be a grid or diffuser that does not allow particles to pass downwards but allows the gas flow to pass upwards.

A fluidizing gas 204 is blown into the bottom 206 of the reactor, the flow rate of which is such that it must allow the fluidization of the mixture of particles. The gas flow leads to a mixing which promotes the movement of the mixture of particles and heat transfer. In the reactor, the PMMA-based matrix is depolymerized by the action of heat, producing in particular gaseous methyl methacrylate monomers. The gases 207 produced in the reactor are conveyed to a gas/solid separator 208, such as a cyclone. Such a separator can be internal or external to the reactor. There can be multiple internal and external separators in series, the first one having the purpose of keeping the inert particles in the reactor and the second one having the purpose of recovering the reinforcement particles 209.

To recover the heat stored in the reinforcement 209, the reinforcement is recovered in a chamber 210 provided for recovering the reinforcement after separation. The chamber 210 is isolated from the separator 208 by any suitable means to potentially prevent the gases produced in the reactor from following the same path as the reinforcement. This can be achieved using an endless screw, an airlock, an inert gas flow creating back pressure, or any other means. The reinforcement has a temperature substantially equal to that in the reactor since it is recovered after the depolymerization process has been carried out in the reactor. The chamber 210 may have an inlet 211 equipped with means for regulating the inflow of the heat transfer fluid into the chamber 210. The chamber may also have an outlet 212 allowing the heated heat transfer fluid to be discharged. In the case of a liquid fluid such as water, the latter is transferred to the chamber 210 from an external reservoir 213.

The fluid may be transported by any suitable means, for example, flexible or rigid ducts or pipes.

Water is introduced into the chamber 210 through the inlet 211. In the illustrated example, the hot reinforcing material 209 is brought into contact with the water entering through the inlet 211, preferably by spraying, and/or by immersion. After the fluid comes into contact with the reinforcing material, heat transfer takes place, resulting in the production of hot steam 214. The heat thus recovered in the form of hot steam is extracted from the chamber 210 through the outlet 212.

Advantageously, the recovered heat can be used in the recycling method of the invention in addition to the heat injected by an external heat source. Heat source is understood to mean all the examples of heating means already described.

For example, this heat can be used in situ for pre-heating 215 of the article 201. The recovered heat can also be used in the monomer purification process. For example, the gas 202 can be condensed using a condenser and the resulting condensate can be hydrolyzed with hot steam. This hot steam can be obtained by heating an aqueous solution, the heating being carried out with recycled heat. The hydrolysis can also be carried out by direct contact of the condensate or steam 207 with water and steam obtained by contacting the hot reinforcement with hot reinforcement, in the presence or absence of a hydrolysis catalyst. The hydrolysis products can then be separated, for example, by crystallization or by any other equivalent technique.

3, the heat exchanger 300 may be a plate-type exchanger with several plates (301a and 301b). These plates 301a and 301b are hollow and may be of approximately rectangular or circular shape, or of cylindrical or semi-cylindrical shape (e.g. troughs). In one example, they are arranged parallel to each other, more precisely flat and one above the other. The gaps between the plates are small, on the order of a few millimeters to a few centimeters, but allow the flow of the reinforcement. Each plate 302 has an internal space in which a heat transfer fluid circulates. The first fluid 302 entering the first plate 301a may have a temperature T1e different from the temperature T2e of the second fluid 303 entering the second plate 301b. The hot reinforcement 209 may be placed on the first plate resting on it by gravity, so that the heat transfer occurs by heat conduction through the upper wall of the plate. The solid residue (i.e., the reinforcement) is transferred from one plate to the next by gravity or by a "pusher" that moves the solid residue (i.e., the reinforcement) forward on the plate. The contact time between the reinforcement and the heat transfer means can be between 100°C and 450°C, between 1 minute and 10 hours.

After a certain time, the reinforcement is moved by means of a means of setting the movement towards a second plate, which also rests on it by gravity. The movement can be continuous or discontinuous. Heat transfer then occurs by the fluid 303 in the second plate. Alternatively, the reinforcement can be set in motion using a pusher, an endless screw, or by gravity. There are several forms of heat exchanger. For example, in the case of stacked circular plates, a scraper is present along the central axis, which can advance the reinforcement along the plate. Each plate has an outlet, which allows the reinforcement to fall at a lower height onto a plate of different temperature. In the case of rectangular plates, which may be slightly inclined, each plate has a scraper that can advance the reinforcement. When the end of the plate is reached, the reinforcement moves to another plate, while the scraper passes under the plate to make a complete circuit of the plate. When an extruder/conveyor is used, the extruder/conveyor can have a section that is heated independently, so that, conversely, at the end of the extruder/conveyor, the section can be cooled independently.

Thus, the other plates can be used successively with the same batch of reinforcement to carry out the heat transfer successively with respective decreasing heat levels. Advantageously, the fluid leaving the first plate 301a has a temperature T1s and the fluid leaving the second plate 301b has a temperature T2s, the temperatures T1s and T2s being different. In this way, the plate type heat exchanger allows the recovery of fluids at the outlets of the plates with different temperatures, or even the same fluid flowing in countercurrent from one plate to the next. Depending on the desired application for the heating fluid to be recovered in the application considered, depending on the temperature of the reinforcement deposited on the plate, the retention time of the reinforcement on the plate and the thermal properties of the latter, the fluid inlet temperature can be selected to obtain an outlet temperature of a given order.

In one embodiment, the heat transfer means, e.g. the first heat transfer means, is suitable for determining the movement of the fibrous reinforcement during heat transfer. To minimize the effect of the movement of the reinforcement on the heat transfer means, a protective agent may be added to the reinforcement. Advantageously, the protective agent also makes it possible to facilitate heat exchange between the reinforcement and the heat transfer means.

Now, a second embodiment of the recycling method in the form of a process diagram is presented. With reference to FIG. 4, the items to be recycled originating from household waste are sorted in step 410. Then, in step 420, the items containing composite material are crushed to produce particles of about 20 mm. In step 110, the crushed particles are fed into a pyrolysis reactor using a metering module at a flow rate of 50 kg/h. The pyrolysis reactor is heated in step 120 at a temperature between 300° C. and 550° C. Under the effect of heat, the polymer matrix depolymerizes to produce a molten mixture and a solid containing the reinforcement. The reinforcement is separated from the molten mixture in step 130 using a separation means. In step 140, the reinforcement with the stored heat is placed in a plate type heat exchanger so that the stored heat can be recovered. The recovered heat can be used in step 430 for preheating the items after crushing.

According to one variant, the recycling method includes a step in which the reinforcement is brought into contact with a first heat transfer means, and then the movement of the reinforcement is determined and moved towards a second heat transfer means. This may, for example, make it possible to recover additional heat after recovering a first amount of heat by contacting the reinforcement (e.g. fibrous reinforcement) with a first heat exchanger. Thus, several transfer means may be used to optimize the heat recovery.

It should be noted that the energy recovered by this method depends on the fiber content of the material and the degree of polymer conversion. Examples of this characteristic are shown in Table 1.

Thus, the recycling method with improved energy balance is particularly suitable for energy recovery when the composite material contains more than 70% fibers and/or when the method does not allow a degree of conversion of the polymer of more than 70%. In particular, under these conditions, more than 40% of the required energy can be recovered, especially when the composite material contains more than 70% fibers and the method allows a degree of conversion of the polymer of less than 70%.

The method is particularly advantageous for recycling composite materials with heat recovery when the fiber content is greater than 40%, allowing recovery of more than 10% of the energy required, regardless of the degree of conversion.

Finally, the overall energy balance can be improved, for example at low fiber content and high conversion degree, by recovering the energy of complete or partial combustion of the unconverted polymer and the energy of combustion of impurities separated from the depolymerized monomers. Partial conversion/combustion/oxidation of the polymer is understood to mean both a less than complete conversion including polymer residues and an oxidation leading to products other than _CO2 , such as CO, acids and light aldehydes, as well as hydrocarbons.

The present invention thus proposes a simple and effective solution for depolymerizing the constituent polymers of composite articles, improving the energy balance and in particular making it possible to recover the heat absorbed by the solid non-depolymerizable fibrous material. This method makes it possible to implement a recycling of articles containing composite materials that reduces the carbon footprint and therefore is more environmentally friendly.

Claims (26)

1. A method for recycling an article comprising a composite material, the composite material comprising a polymer matrix and a reinforcement material, the method comprising the steps of:
- placing the article in a reactor suitable for heating the article (110);
- heating the article in the reactor at a predetermined temperature to decompose the polymer matrix (120);
- separating the reinforcement from the decomposed polymer matrix (130), and - contacting the reinforcement with a first heat transfer means (140) to recover heat.
The method according to claim 1, further comprising: The recycling method of claim 1, characterized in that the items are introduced into the reactor by an endless screw, a conveyor belt, a hopper or a weighing module. The recycling method according to claim 1 or 2, characterized in that the article is heated at a temperature between 200°C and 1500°C. The recycling method according to any one of claims 1 to 3, characterized in that the reinforcing material is separated by at least one of the following processes: centrifugation, draining, spinning, pressing, filtering, screening and/or cyclones. The recycling method according to any one of claims 1 to 4, characterized in that the first heat transfer means is a heat exchanger in which there is direct contact between the reinforcing material and the heat transfer fluid. The recycling method according to claim 5, characterized in that the first heat transfer means is a device for immersion in a heat transfer fluid or for spraying the heat transfer fluid. The recycling method according to any one of claims 1 to 4, characterized in that the first heat transfer means is a heat exchanger in which there is indirect contact between the reinforcing material and the heat transfer fluid. The recycling method according to any one of claims 1 to 7, characterized in that a protective agent is added to the reinforcing material. The recycling method according to any one of claims 1 to 8, characterized in that the recovered heat is used in the article recycling method in addition to the heat injected by an external heat source. The recycling method according to any one of claims 1 to 9, characterized in that the recovered heat is used to preheat the items before they are introduced into the reactor. The recycling method according to any one of claims 1 to 10, characterized in that after the heat recovery by contacting the reinforcing material with the first heat transfer means, the method further comprises the step of contacting the reinforcing material with a second heat transfer means to recover additional heat. The recycling method according to any one of claims 1 to 11, characterized in that the decomposition of the composite material comprising the polymer matrix and the reinforcing material is carried out by a method selected from pyrolysis, high-temperature pyrolysis, heat treatment in a fluidized bed reactor, heat treatment in an extruder or conveyor, heat treatment in a rotary furnace, pyrolysis in a mechanically stirred bed, pyrolysis in a molten salt bath, or depolymerization by solvolysis including temperature increase. The recycling method according to any one of claims 1 to 12, characterized in that the polymer matrix is a matrix made of a thermosetting polymer or a thermoplastic polymer. The polymer matrix may be selected from the group consisting of olefin homopolymers and copolymers, such as acrylonitrile-butadiene-styrene copolymers, styrene-butadiene-alkyl methacrylate (or SBM) copolymers; polyethylene, polypropylene, polybutadiene and polybutylene; acrylic homopolymers and copolymers and polyalkyl methacrylates, such as poly(methyl methacrylate); homopolyamides and copolyamides; polycarbonates; polyesters, including poly(ethylene terephthalate) and poly(butylene terephthalate); poly(phenylene ether), poly(oxymethylene), poly(oxyethylene) or poly(ethylene glycol) and poly(oxypropane); 13. The recycling method according to any one of claims 1 to 12, characterized in that the polymer is selected from the group consisting of polyethers such as poly(vinyl chloride), polystyrene, copolymers of styrene and maleic anhydride, fluoropolymers such as poly(vinylidene fluoride), polyethylene tetrafluoride and polychlorotrifluoroethylene, natural or synthetic rubbers, thermoplastic polyurethanes, polyaryletherketones (PAEKs) such as polyetheretherketones (PEEK) and polyetherketoneketones (PEKK), polyetherimides, polysulfones, poly(phenylene sulfide), cellulose acetate, poly(vinyl acetate), or mixtures of two or more of these polymers. The recycling method according to any one of claims 1 to 12, characterized in that the polymer matrix contains polymethyl methacrylate (PMMA). The recycling method according to any one of claims 1 to 15, characterized in that a part of the decomposed matrix is separated from the reinforcing material and then reintroduced into the reactor. The recycling method according to any one of claims 1 to 16, characterized in that the composite material contains more than 40% by weight of reinforcing material. The recycling method according to any one of claims 1 to 16, characterized in that the composite material contains more than 70% by weight of reinforcing material. The recycling method according to any one of claims 1 to 18, characterized in that the recovered heat is recovered at one or more heat levels. The method for recycling articles according to any one of claims 1 to 19, characterized in that the method includes a preliminary sorting step before carrying out the method. The recycling method according to any one of claims 1 to 19, characterized in that the items are fed into the reactor at a flow rate that supplies the reactor with between 10 kg/h and 2000 kg/h of the items to be recycled. The recycling method according to any one of claims 1 to 19, characterized in that the method includes a step of crushing the article. The recycling method according to any one of claims 1 to 19, characterized in that the recycling method includes a step of preheating the item to be recycled. 1. A system for recycling an article comprising a composite material having a polymer matrix and a reinforcement, comprising:
- means for conveying said items,
a reactor suitable for heating said article in order to decompose its polymer matrix;
- means for separating the reinforcement from the decomposed polymer matrix; and - first heat transfer means suitable for recovering heat from the reinforcement. The recycling system of claim 24, further comprising a second heat transfer means capable of recovering additional heat from the reinforcement material. 25. The recycling system of claim 24, wherein the separating means is in one of the following forms: a centrifuge, a draining means, a spinning means, a pressing means, a filter, a screen and/or a cyclone.